1. Field of the Invention
This invention relates to a toner used in recording processes such as electrophotography, electrostatic recording, magnetic recording and toner jet recording, and an image-forming apparatus, a process cartridge and an image-forming method which make use of the toner; the image-forming method being a method of forming a fixed image by heat and pressure fixing a toner image formed on a transfer medium.
2. Related Background Art
A number of methods as disclosed in U.S. Pat. No. 2,297,691, Japanese Patent Publications No. 42-23910 and No. 43-24748 and so forth are conventionally known as methods for electrophotography. In general, copies are obtained by forming an electric latent image (electrostatic latent image) on a photosensitive member by various means utilizing a photoconductive material, subsequently developing the latent image by the use of a toner to form a toner image, and transferring the toner image to a transfer medium (recording medium) such as paper as occasion calls, followed by fixing by the action of heat, pressure, heat-and-pressure, or solvent vapor. The toner that has not transferred and has remained on the photosensitive member is cleaned by various means, and then the above process is repeated.
In recent years, as a reflection of changing commercial needs for making composite, personal and so forth, such copying machines are severely sought to be made more small-sized, more light-weight, more high-speed and more highly reliable. As the result, performances required for toners have also become high-level.
In particular, one-component development making use of magnetic toners is preferably used because of its developing assembly having a simple structure, which may cause less troubles, has a long lifetime and may require only easy maintenance service.
Still in recent years, image-forming apparatus employing an electrophotographic technique, such as copying machines and laser beam printers, have been made to have various functions, and toner images to be formed are sought to be of high precision and high image quality. Accordingly, used are toners suited therefor and process cartridges making use of such toners.
For example, Japanese Patent Publication No. 51-23354 discloses a toner comprising a vinyl polymer cross-linked to an appropriate degree by adding a cross-linking agent and a molecular weight modifier. Also proposed in a large number are toners of a blend type comprising a vinyl polymer in which its Tg, molecular weight and gel content are specified in combination.
Such toners containing a cross-linked vinyl polymer or a gel content have an excellent effect on anti-offset properties. However, where such a cross-linked vinyl polymer is used in order to incorporate it in a toner, the polymer may have a very great internal friction in the step of melt kneading when the toner is produced, and a large shear force is applied to the polymer. Hence, in many cases, the cutting of molecular chains occurs to cause a decrease in melt viscosity, and this may adversely affect the anti-offset properties.
Accordingly, to solve this problem, it is proposed, as disclosed in Japanese Patent Applications Laid-open No. 55-90509, No. 57-178249, No., 57-178250 and No. 60-4946, that, a resin having a carboxylic acid and a metal compound are used as toner materials and are heated and reacted at the time of melt kneading to form a cross-linked polymer, which is then incorporated into the toner.
Japanese Patent Applications Laid-open No. 61-110155 and No. 61-110156 also disclose that a binder having as essential constituent units a vinyl resin monomer and also a special monoester compound is allowed to react with a polyvalent metal compound to carry out cross-linking through a metal.
Japanese Patent Applications Laid-open No. 63-214760, No. 63-217362, No. 63-217363 and No. 63-217364 still also disclose that a binder resin has a molecular weight distribution separated into two groups, a low-molecular weight region and a high-molecular weight region, and carboxylic acid groups incorporated into the low-molecular weight region side are allowed to react with polyvalent metal ions to carry out cross-linking (a dispersion of a metal compound is added in a solution obtained by solution polymerization, followed by heating to carry out the reaction).
Japanese Patent Applications Laid-open No. 2-168264, No. 2-235069, No. 5-173363, No. 5-173366 and No. 5-241371 still also disclose toner binder compositions and toners in which the molecular weights, mixing ratio, acid values and their percentages of a low-molecular weight component and a high-molecular weight component in a binder resin are controlled to improve fixing performance and anti-offset properties.
Japanese Patent Application Laid-open No. 62-9256 still also discloses a toner binder composition comprising a blend of two kinds of vinyl resins having different molecular weights and acid values of resin.
Japanese Patent Applications Laid-open No. 3-63661, No. 3-63662, No. 3-63663 and No. 3-18552 still also disclose that a carboxyl-group-containing vinyl copolymer and an epoxy-group-containing vinyl copolymer are allowed to react with a metal compound to carry out cross-linking.
Japanese Patent Applications Laid-open No. 7-225491 and No. 8-44107 still also disclose that a carboxyl-group-containing resin reacts with an epoxy resin to form a cross-linked structure.
Japanese Patent Applications Laid-open No. 62-194260, No. 6-11890, No. 6-222612, No. 7-20654, No. 9-185182, No. 9-244295, No. 9-319410, No. 10-87837 and No. 10-90943 still also disclose toner binder compositions and toners in which molecular weight distribution, gel content, acid value and epoxy value are controlled in a resin composition constituted of a carboxyl-group-containing resin, using a glycidyl-group-containing resin as a cross-linking agent, to improve fixing performance and anti-offset properties.
These proposals disclosed as shown above, though having merits and demerits, have in fact attained good effects with respect to the improvement in anti-offset properties. There, however, are problems in developing performance and running performance when applied to magnetic toners for one-component development. Thus, a further improvement is required.
Japanese Patent Applications Laid-open No. 1-257968, No. 4-124681 and No. 6-51556 also disclose magnetic toners whose dielectric dissipation factor has been controlled to provide toners having good chargeability.
In the above proposal, however, there is a problem when applied in high-speed machines having a large copy volume, and a further improvement is required in order to improve the dispersibility of resins and magnetic materials.
As stated in the above proposals, the quality of image formation depends greatly on charging performance of magnetic toners. In the magnetic toners, a magnetic material is incorporated into a toner to endow the toner with magnetic properties. Also, part of the magnetic material stands liberated from toner particles or uncovered to their surfaces, and hence it influences the fluidity of magnetic toner and the triboelectric chargeability with a charging member in a developing assembly to influence developing performance and running performance. In particular, in recent years, a high running performance is required as a performance of the magnetic toner, and hence it is difficult to achieve both the properties of a resin and the dispersibility of a magnetic material which are used in toner particles. Especially when a cross-linked type resin is used, a further improvement is required for resin materials and magnetic materials.
Many proposals have been made on the magnetic materials. For example, a magnetic material incorporated with silicon and zinc is proposed in Japanese Patent Application Laid-open No. 8-101529; magnetic materials incorporated with silicon are proposed in Japanese Patent Applications Laid-open No. 7-175262, No. 5-72801, No. 62-278131, No. 61-34070, No. 8-25747, No. 9-59024 and No. 9-59025; magnetic materials incorporated with silicon and aluminum are proposed in Japanese Patent Applications Laid-open No. 7-110598 and No. 5-281778; and a magnetic toner making use of a magnetic material incorporated with magnesium is proposed in Japanese Patent Application Laid-open No. 5-345616. Good developing performance has been attained in these proposals. However, when used in positively chargeable magnetic toners, when used in high-speed machines and when copies are taken in a very large volume over a long period of time with repetition of toner supply, it is long awaited to further improve developing performance of toners and to improve running performance, e.g., prevent the magnetic material from being liberated from toner particles.
Thus, in order to prevent the magnetic material from being liberated from toner particles, the improvement of magnetic materials alone has a limit, and the improvement of binder resins to be used is also required.
Meanwhile, various methods and apparatus have been developed with regard to the step of fixing toner images to sheets such as paper. A fixing method most common at present is a pressure heating method making use of a fixing unit which fixes toner images through a pressure roller by means of a fixing roller having a stationary heater.
In this fixing unit, the fixing roller is formed in a hollow body. On the axis of this fixing roller, a heating medium is held by a holding means. The heating medium is constituted of, e.g., a tubular heater such as a halogen lamp, and generates heat upon application of a stated voltage. Since the halogen lamp is positioned on the axis of the fixing roller, the heat generated from the halogen lamp is uniformly radiated against the inner wall of the fixing roller, so that the outer wall of the fixing roller has a temperature distribution which is uniform in the circumferential direction. The outer wall of the fixing roller is heated until its temperature reaches a temperature suited to fixing (e.g., 150 to 200xc2x0 C.). In this state, the fixing roller and the pressure roller are rotated in the directions opposite to each other while coming into pressure contact, and hold between them a sheet to which a toner image has adhered. At a pressure contact zone (hereinafter also xe2x80x9cnipxe2x80x9d) between the fixing roller and the pressure roller, the toner image on the sheet is melted by the heat of the fixing roller and is fixed to the sheet by the pressure acting from both rollers.
However, since in the above fixing unit having the heating medium constituted of a halogen lamp the fixing roller is heated by utilizing the heat radiated from the halogen lamp, it takes a relatively long time as the time by which the temperature of the fixing roller reaches the stated temperature suited to fixing after a power source has been put on (hereinafter xe2x80x9cwarm-up timexe2x80x9d). During that time, users can not use the copying machine and are compelled to wait for a long time. There has been such a problem.
On the other hand, application of electric power to the fixing roller in a large quantity in order to improve user""s operability in an attempt to shorten the warm-up time results in an increase in power consumption in the fixing unit, bringing about a problem that this goes against energy saving. Accordingly, in order to make copying machines and so forth have a higher commercial value, it has more attracted notice and been considered important to achieve both the energy saving of the fixing unit (i.e., low power consumption) and the improvement in user""s operability (i.e., quick printing).
As a unit that meets such a demand, a fixing unit of an induction heating type which utilizes high-frequency induction as a heating source is proposed as disclosed in Japanese Patent Application Laid-open No. 59-33787. This induction heating fixing unit comprises a hollow fixing roller made of a metallic conductor, in the interior of which a coil is provided in a concentric form. To this coil, a high-frequency electric current is flowed to form a high-frequency magnetic field, through which the fixing roller is caused to generate an induction eddy current so that the fixing roller itself can be brought into generation of Joule heat on account of the skin resistance of the fixing roller itself. This fixing unit of an induction heating type makes it possible to shorten the warm-up time because of a great improvement in electricity-heat conversion efficiency.
A core (magnetic-field barrier member) comprised of a magnetic material may also be used in the coil in combination, whereby the high-frequency magnetic field can efficiently be formed. Especially when a core having a T-shaped cross section is used, the heat in an amount necessary as the fixing unit can be generated by a low electric power on account of the efficient convergence of the high-frequency magnetic field and the effect of shielding the part other than the heat-generating portion from the magnetic field.
However, in the conventional case as stated above, there has been a problem as stated below. In the above fixing unit of an induction heating type, in order to make the most of a strong point that the time taken until the surface temperature of the fixing roller reaches the temperature suited to fixing can be shortened when the fixing unit has started operating, it is better for the fixing roller to have a heat capacity as small as possible. Use of a fixing roller having a small wall thickness for that purpose makes it difficult to set high the pressing force at the fixing nip because of a rigidity of the fixing member, making it difficult to set low the fixing temperature. Also, in this case, the heat is transmitted with difficulty in the direction of the rotating shaft of the fixing roller. For example, when small-sized sheets of paper are continuously fed to pass, the fixing roller tends to have a large difference in temperature between the paper pass area and the paper non-pass area. Here, any temperature control made at the paper pass area of the fixing roller may make the paper non-pass area have a greatly higher temperature than the temperature suited to fixing, to tend to cause the offset of toner to the fixing roller surface at the paper non-pass area or cause paper jam because of the winding of paper around the fixing roller.
The high-frequency magnetic field formed by flowing the high-frequency electric current to the coil may also slightly leak from the magnetic-field barrier member to tend to disorder unfixed magnetic toner images on the transfer medium before their rush into the fixing unit, to cause xe2x80x9cspots around line images at fixingxe2x80x9d. Such a problem may be solved by increasing the transfer electric current at the time of transfer in order to make stronger the electrostatic force acting between the toner and the transfer medium. This, however, may cause a difficulty that the discharge current under a high electric field comes around to the photosensitive member to roughen the photosensitive member surface to shorten the lifetime of the photosensitive member.
In addition, in the system making use of the fixing unit of an induction heating type, part of the magnetic material liberated as stated previously tends to disorder the unfixed toner images because of the high-frequency magnetic field which leaks from the fixing unit.
As discussed above, the toners used in the one-component development method and in the fixing method of an induction heating type have become required to have higher performances than those used in other methods, and are required to be much more improved in developing performance, fixing performance and anti-offset properties.
An object of the present invention is to solve the above problems to provide a toner having superior developing performance and running performance, and an image-forming apparatus and a process cartridge which develop electrostatic latent images by the use of the toner.
Another object of the present invention is to provide a toner which has superior low-temperature fixing performance and high-temperature anti-offset properties in low-speed processing up to high-speed processing and can form sharp images without causing any spots around line images at fixing, even when toner images on a transfer medium (recording medium) are heat-fixed by an electromagnetic induction heating method to form fixed images on the transfer medium.
Still another object of the present invention is to provide an image-forming method which can achieve both the energy saving of the fixing unit (i.e., low power consumption) and the improvement in user""s operability (i.e., quick printing).
The present invention provides a toner comprising a binder resin and a colorant, wherein;
the toner contains as the binder resin at least a vinyl resin selected from the group consisting of:
a vinyl resin having a carboxyl group and a vinyl resin having an epoxy group;
a vinyl resin having a carboxyl group and an epoxy group; and
a vinyl resin produced by the reaction of a carboxyl group with an epoxy group; and
the toner has, in its dielectric dissipation factor (tan xcex4), at least a maximum value and a minimum value in the temperature range of from 20xc2x0 C. to 150xc2x0 C., and, where the maximum value is represented by Max and the minimum value by Min, has a value of log10(Max/Min)xe2x89xa62.
The present invention also provides an image-forming apparatus comprising a developing means for moving a toner to an electrostatic latent image formed on a photosensitive member, to render the electrostatic latent image visible to form a toner image, and a transfer means for transferring the toner image to a transfer medium to form an image;
in a developer-carrying member of said developing means, at least an alternating-current bias being applied to make the toner adhere to the electrostatic latent image to form a visible image; and
the toner comprising a binder resin and a colorant;
wherein;
the toner contains as the binder resin at least a vinyl resin selected from the group consisting of:
a vinyl resin having a carboxyl group and a vinyl resin having an epoxy group;
a vinyl resin having a carboxyl group and an epoxy group; and
a vinyl resin produced by the reaction of a carboxyl group with an epoxy group; and
the toner has, in its dielectric dissipation factor (tan xcex4), at least a maximum value and a minimum value in the temperature range of from 20xc2x0 C. to 150xc2x0 C., and, where the maximum value is represented by Max and the minimum value by Min, having a value of log10(Max/Min)xe2x89xa62.
The present invention still also provides a process cartridge which is used in an image-forming apparatus in which a toner is moved to an electrostatic latent image formed on a photosensitive member, to render the electrostatic latent image visible to form a toner image, and the toner image is transferred to a transfer medium to form an image; the process cartridge being detachably mountable to the image-forming apparatus;
the photosensitive member and at least one means selected from a charging means for charging the photosensitive member electrostatically, a latent-image-forming means for forming the electrostatic latent image on the photosensitive member, a transfer means for transferring the toner image to the transfer medium and a cleaning means for removing a toner having remained on the photosensitive member after the toner image has been transferred to the transfer medium being supported as one unit together with a developing means by which the electrostatic latent image formed on the photosensitive member is developed with the toner to form the toner image;
in a developer-carrying member of the developing means, at least an alternating-current bias being applied to make the toner adhere to the electrostatic latent image to form a visible image; and
the toner comprising a binder resin and a colorant;
wherein;
the toner contains as the binder resin at least a vinyl resin selected from the group consisting of:
a vinyl resin having a carboxyl group and a vinyl resin having an epoxy group;
a vinyl resin having a carboxyl group and an epoxy group; and
a vinyl resin produced by the reaction of a carboxyl group with an epoxy group; and
the toner has, in its dielectric dissipation factor (tan xcex4), at least a maximum value and a minimum value in the temperature range of from 20xc2x0 C. to 150xc2x0 C., and, where the maximum value is represented by Max and the minimum value by Min, having a value of log10(Max/Min)xe2x89xa62.
The present invention further provides an image-forming method comprising subjecting a toner image held on a transfer medium, to heat-and-pressure fixing by a heat-and-pressure fixing means to form a fixed image on the transfer medium, wherein;
(1) a toner which forms the toner image is a toner comprising a binder resin and a colorant;
the toner containing as the binder resin at least a vinyl resin selected from the group consisting of:
a vinyl resin having a carboxyl group and a vinyl resin having an epoxy group;
a vinyl resin having a carboxyl group and an epoxy group; and
a vinyl resin produced by the reaction of a carboxyl group with an epoxy group; and
the toner having, in its dielectric dissipation factor (tan xcex4), at least a maximum value and a minimum value in the temperature range of from 20xc2x0 C. to 150xc2x0 C., and, where the maximum value is represented by Max and the minimum value by Min, having a value of log10(Max/Min)xe2x89xa62; and
(2) as the heat-and-pressure fixing means, a heat-and-pressure fixing means is used which has at least;
(i) a magnetic field generation means;
(ii) a rotary heating member having at least a heat generation layer capable of generating heat by electromagnetic induction and a release layer; and
(iii) a rotary pressure member which forms a nip with the heating member; and
the toner image held on the transfer medium is heat and pressure fixed while the rotary pressing member is pressed against the rotary heating member via the transfer medium.